The importance of accurately monitoring and controlling the flow of fibers being fed to a carding machine is well recognized by those skilled in the art. A number of less than satisfactory attempts have been made at providing devices capable of performing this important function. Many of these devices attempt to measure flow rate indirectly as a function of the ability of the fiber condition to absorb or reflect either sound, light or isotropic radiation. The principal problem with such devices, however, is that the absorption capabilities of fibers varies widely, depending for example on fiber type (nylon, polyester, wool, etc.), the content of fiber blends, fiber lustre or colors, the application of emulsion, tints or anti-stats, etc. Thus, such devices require frequent recalibration, with attendant flow rate inaccuracies during the continuing operation.
Another known device measures the nip pressure exerted by a pair of rolls acting on the fiber flow. However, the accuracy of this type of device is compromised whenever randomly distributed lumps of fibers pass between the rolls, causing deceptive pressure increases which are not truly representative of the total fiber flow.